1. Field of the Invention
The present invention relates to an image forming apparatus and a control method thereof.
2. Description of the Related Art
Recently, in the field of image forming apparatuses using electrophotographic technology, there are constant demands for reductions in size and cost. To realize such reductions in size and cost, a method has been discussed (see Japanese Patent Application Laid-Open No. 07-175005) which uses a galvanomirror fabricated by a semiconductor fabrication technique instead of a conventionally-used polygonal mirror. In this method, an image is formed by making the mirror resonate at a specific resonant frequency which is based on the mechanical dimensions of the galvanomirror, and by scanning a light beam in the main scanning direction.
Further, for a nested mirror (Japanese Patent Application Laid-Open No. 2005-208578), there are the qualities that the available scanning area is considered a constant angular velocity, and that the scanning angle can be made larger. As a result, a correction optical system can be made to have a compact and simple structure, which is suitable for a scanning apparatus in a compact, low-cost image forming apparatus.
If a light beam is deflected using a technique such as that described above to make a vibrating mirror resonate, wobbles occur in the resonance due to turbulence or the like caused by air resistance during the resonance operation. The wobbles can produce non-periodic jitter.
This jitter becomes apparent as angular velocity jitter of the vibrating mirror and image forming position jitter in the main scanning direction such as that illustrated in FIG. 2A, which causes a difference in the width of the main scanning direction. This results in shake in the straight lines of the sub-scanning direction at the center and at the edges on the transfer medium, so that image quality deteriorates.